It's Topic Tuesday!

Welcome back to another Topic Tuesday! I'm Alvaro. This week, we will discuss a topic revolutionizing anticoagulation: NOACs—Novel Oral Anticoagulants. Let's explore what they are, how they work, and why they're not used in certain situations, like mechanical heart valves.

What are NOACs?

NOACs, or Novel Oral Anticoagulants (sometimes called DOACs—Direct Oral Anticoagulants), are a newer class of blood thinners that include drugs like apixaban, rivaroxaban, dabigatran, and edoxaban. These medications are used to prevent blood clots.

Unlike warfarin, the old-school vitamin K antagonist, NOACs directly target specific clotting factors. For example, rivaroxaban and apixaban inhibit factor Xa, while dabigatran inhibits thrombin (factor IIa).

Imagine you're managing a busy hospital break room, and people need coffee all day long (just like your body needs blood to flow smoothly without clots). There are two ways to keep the coffee flowing:

1. Warfarin = The Old Manual Coffee Maker

This machine needs a lot of adjusting. You must grind the beans, measure the water precisely, and check the taste constantly (like INR monitoring). If you mess up even a little, the coffee might be too weak (bleeding risk) or too strong (clotting risk).

2. NOACs = The New Smart Coffee Machine

This one is pre-programmed. You just hit a button, and it makes great coffee every time. No need to check, adjust, or monitor—it knows how much water and coffee to use.

NOACs don't need INR monitoring and still prevent clots effectively in most patients.

But... What if you use the wrong coffee pods?

Let's say your new machine can't handle the old-school metal pods used for exceptional coffee. You try it anyway, but the machine malfunctions or leaks.

That's what happens when you use NOACs in mechanical heart valves. The valves are made of metal and change the flow in the heart—NOACs just weren't built to work with them, and using them can cause serious problems (like in the RE-ALIGN trial).

☠️ In this case, you must return to the manual coffee maker—warfarin.

Do NOACs Require INR Monitoring?

One of the biggest game-changers with NOACs is no routine INR (International Normalized Ratio) monitoring. Warfarin requires frequent blood tests to make sure you're within the therapeutic range. With NOACs, the dosing is fixed and predictable, meaning no dietary restrictions, fewer drug interactions, and greater patient convenience.

Why Can't NOACs Be Used in Mechanical Valves?

Now, here's where things get interesting—and crucial. While NOACs are great for atrial fibrillation and venous thromboembolism, they are not recommended for patients with mechanical heart valves.

Why? Because the RE-ALIGN trial, which studied dabigatran in patients with mechanical valves, had to be stopped early. Patients on dabigatran had higher rates of thromboembolic events and bleeding compared to those on warfarin. The mechanical surface of the valve creates a unique risk of clotting that NOACs can't handle. So, warfarin remains the gold standard for mechanical valves.

So Where Do NOACs Fit In?

Excellent option for non-valvular atrial fibrillation

First-line treatment for DVT and PE

Not used in pregnancy, mechanical valves, or specific severe renal impairments

In Summary:

NOACs have simplified anticoagulation for many patients by eliminating the need for INR monitoring and offering fewer dietary restrictions. But remember, they're not for everyone—especially not for those with mechanical heart valves. In those cases, the classic warfarin is still king.

That's it for today, folks! Stay curious, and we'll see you back next Tuesday for another exciting topic.

ATT:

ALVARO JOSE MARTINEZ SANTACRUZ

Bibliography

[1] Eikelboom JW, Connolly SJ, Brueckmann M, Granger CB, Kappetein AP, Mack MJ, et al. Dabigatran versus warfarin in patients with mechanical heart valves. N Engl J Med 2013;369:1206–14. https://doi.org/10.1056/NEJMoa1300615.

[2] Bauer KA. Pros and cons of new oral anticoagulants. Hematology Am Soc Hematol Educ Program 2013;2013:464–70. https://doi.org/10.1182/asheducation-2013.1.464.

[3] Paul C, Baby M, Anthraper AR, Krishnakumar. NOACs: an emerging class of oral anticoagulants review article. Futur J Pharm Sci 2020;6. https://doi.org/10.1186/s43094-020-00114-1.